Fabrication of a vertical field effect transistor device with a modified vertical fin geometry

ABSTRACT

A vertical transport fin field effect transistor (VTFET) with a smaller cross-sectional area at the top of the fin than at the bottom, including, a substrate, a vertical fin on the substrate, wherein the vertical fin has a cross-sectional area at the base of the vertical fin that is larger than a cross-sectional area at the top of the vertical fin, wherein the cross-sectional area at the top of the vertical fin is in the range of about 10% to about 75% of the cross-sectional area at the base of the vertical fin, and a central gated region between the base and the top of the vertical fin.

BACKGROUND Technical Field

The present invention generally relates to a fabrication process and anintegrated circuit device structure having a reduced top source/draincapacitance and a reduced bottom source/drain resistance, and moreparticularly to a vertical transport fin field effect transistor (VTFET)having a smaller channel-to-top drain contact area and a largerchannel-to-bottom source contact area.

Description of the Related Art

A Field Effect Transistor (FET) typically has a source, a channel, and adrain, where current flows from the source to the drain, and a gate thatcontrols the flow of current through the channel. Field EffectTransistors (FETs) can have a variety of different structures, forexample, FETs have been fabricated with the source, channel, and drainformed in the substrate material itself, where the current flowshorizontally (i.e., in the plane of the substrate), and finFETs havebeen formed with the channel extending outward from the substrate, butwhere the current also flows horizontally from a source to a drain. Thechannel for the finFET can be an upright slab of thin approximatelyrectangular silicon (Si), commonly referred to as the fin with a gate onthe fin, as compared to a MOSFET with a single gate in the plane of thesubstrate. Depending on the doping of the source and drain, an n-FET ora p-FET can be formed.

Examples of FETs can include a metal-oxide-semiconductor field effecttransistor (MOSFET) and an insulated-gate field-effect transistor(IGFET). Two FETs also can be coupled to form a complementary metaloxide semiconductor (CMOS) device, where a p-channel MOSFET andn-channel MOSFET are coupled together.

With ever decreasing device dimensions, forming the individualcomponents and electrical contacts becomes more difficult. An approachis therefore needed that retains the positive aspects of traditional FETstructures, while overcoming the scaling issues created by formingsmaller device components.

SUMMARY

In accordance with an embodiment of the present invention, a verticaltransport fin field effect transistor (VTFET) with a smallercross-sectional area at the top of the fin than at the bottom,including, a substrate, a vertical fin on the substrate, wherein thevertical fin has a cross-sectional area at the base of the vertical finthat is larger than a cross-sectional area at the top of the verticalfin, wherein the cross-sectional area at the top of the vertical fin isin the range of about 10% to about 75% of the cross-sectional area atthe base of the vertical fin, and a central gated region between thebase and the top of the vertical fin is provided.

In accordance with another embodiment of the present invention, avertical transport fin field effect transistor (VTFET) with a smallercross-sectional area at the top of the fin than at the bottom,including, a substrate, a doped region in the substrate forming a bottomsource, and a vertical fin having two sidewalls separated by athickness, and two end walls separated by a length on the bottom source,wherein the end walls taper from the base of the vertical fin adjacentto the bottom source to the top of the vertical fin opposite the baseand separated by a height of the vertical fin is provided.

In accordance with yet another embodiment of the present invention, amethod of forming a vertical transport fin field effect transistor(VTFET) with a smaller cross-sectional area at the top of the fin thanat the base of the fin, including, forming a vertical fin on asubstrate, wherein the vertical fin has two sidewalls separated by athickness, and two end walls separated by a length, and etching the finto taper at least the end walls, such that the cross-sectional area atthe top of the fin is in the range of about 10% to about 75% of thecross-sectional area at the base of the vertical fin is provided.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description will provide details of preferred embodimentswith reference to the following figures wherein:

FIG. 1 is a cross-sectional side view showing a substrate, in accordancewith an embodiment of the present invention;

FIG. 2 is a cross-sectional side view showing a fin template layerformed on the surface of the substrate, and a fin mask layer formed onthe fin template layer, in accordance with an embodiment of the presentinvention;

FIG. 3 is a cross-sectional side view showing a patterned fin mask layeron a patterned fin template layer, in accordance with an embodiment ofthe present invention;

FIG. 4 is a cross-sectional side view showing a vertical fin formed onthe substrate with a fin template and a fin mask segment on the verticalfin, in accordance with an embodiment of the present invention;

FIG. 5 is a cross-sectional side view showing a spacer layer formed onthe vertical fin and fin template after removal of the fin mask segment,in accordance with an embodiment of the present invention;

FIG. 6 is a cross-sectional side view showing a gate dielectric layerformed on a bottom spacer, vertical fin, and fin template after removalof the portion of the spacer layer on the vertical fin and fin template,in accordance with an embodiment of the present invention;

FIG. 7 is a cross-sectional side view showing a work function layer onthe gate dielectric layer, in accordance with an embodiment of thepresent invention;

FIG. 8 is a cross-sectional side view showing a gate fill layer on thework function layer, in accordance with an embodiment of the presentinvention;

FIG. 9 is a cross-sectional side view showing a gate structure with areduced height gate fill layer, in accordance with an embodiment of thepresent invention;

FIG. 10 is a cross-sectional side view showing a gate structure formedon the vertical fin, and a top spacer formed on the exposed portions ofthe gate structure, in accordance with an embodiment of the presentinvention;

FIG. 11 is a cross-sectional side view showing a vertical fin with anexposed top surface after removal of the fin template, in accordancewith an embodiment of the present invention;

FIG. 12 is a cross-sectional side view showing a top source/drain formedon the vertical fin, in accordance with an embodiment of the presentinvention;

FIG. 13 is an orthographic cut-away view of an exemplary vertical finhaving inclined end walls and sidewalls tapering inwardly in thedirection of the top surface, and a gate structure and top spacer on thevertical fin, in accordance with an embodiment of the present invention;

FIG. 14 is a cross-sectional side view showing a plurality of fin masksegments on each of a plurality of fin template segments patterned toform a series of masked regions, in accordance with an embodiment of thepresent invention;

FIG. 15 is a cross-sectional side view showing a vertical fin formed onthe substrate with fin template segments and fin mask segments separatedby gaps, and notches formed in an upper portion of the vertical fin, inaccordance with an embodiment of the present invention;

FIG. 16 is a cross-sectional side view showing a spacer layer formed onthe vertical fin, fin templates, and in the gaps and notches afterremoval of the fin mask segments, in accordance with an embodiment ofthe present invention;

FIG. 17 is a cross-sectional side view showing a gate dielectric layerformed on a bottom spacer, vertical fin, and fin template after removalof the portion of the spacer layer on the vertical fin and fin template,in accordance with an embodiment of the present invention;

FIG. 18 is a cross-sectional side view showing a work function layer onthe gate dielectric layer, in accordance with an embodiment of thepresent invention;

FIG. 19 is a cross-sectional side view showing a gate fill layer on thework function layer, in accordance with an embodiment of the presentinvention;

FIG. 20 is a cross-sectional side view showing a gate structure with areduced height gate fill layer, in accordance with an embodiment of thepresent invention;

FIG. 21 is a cross-sectional side view showing a gate structure formedon the vertical fin, and a top spacer formed on the exposed portions ofthe gate structure, in accordance with an embodiment of the presentinvention;

FIG. 22 is a cross-sectional side view showing a vertical fin with anexposed top surface and dielectric plugs after removal of the fintemplates, in accordance with an embodiment of the present invention;

FIG. 23 is a cross-sectional side view showing a top source/drain formedon the vertical fin, in accordance with an embodiment of the presentinvention;

FIG. 24 s a cross-sectional side view showing void spaces formed byremoval of the dielectric plugs, and a top source/drain formed on thevertical fin across the void spaces, in accordance with an embodiment ofthe present invention;

FIG. 25 is an orthographic cut-away view of an exemplary vertical finhaving inclined end walls and sidewalls, and notches formed in the upperportion and top surface of the vertical fin, in accordance with anembodiment of the present invention; and

FIG. 26 is a block/flow diagram illustrating a method of forming a VTFETwith reduced drain capacitance and reduced source resistance, inaccordance with an embodiment of the present principles.

DETAILED DESCRIPTION

Principles and embodiments of the present invention relate generally toforming a vertical fin having a modified geometry, where the area of atop surface of the vertical fin intended to be in direct contact with atop source/drain is reduced in comparison with the surface area thevertical fin would have with an unmodified geometry.

Principles and embodiments of the present disclosure are also generallyrelated to a vertical transport field effect transistor (VTFET) having achannel geometry that reduces a channel-to-drain capacitance, whileavoiding an increase in source-to-channel resistance. A verticaltransport field effect transistor (VTFET) can have current flowing froma bottom source vertically through a channel formed by a vertical fin toa top drain. Vertical transistors can have high capacitance due to thelarge interfaces created at the bottom source/drain and the topsource/drain. This capacitance can result in degraded device speed andhigher circuit/chip power usage. It has been recognized that reducingthe contact area at the interface between a VTFET channel and a topdrain can provide a reduced capacitance, which may increase device speed(e.g., switching speed). In addition, it has been recognized thatmaintaining or increasing the contact surface between a VTFET bottomsource and the channel can provide a reduced resistance, which canincrease the device drive current. The combination of a largersource-to-channel contact area and a smaller channel-to-drain contactarea can provide a faster VFET with increased drive current. A reductionin drain size can also reduce drain-induced barrier lowering (DIBL),which may decrease OFF-state current, and/or lower subthreshold-swingvalue. The ratio of the ON-state current to the OFF-state current,I_(on)/I_(off), may also improve.

Exemplary applications/uses to which the present invention can beapplied include, but are not limited to: logic (e.g., NAND, NOR, XOR,etc.) and memory devices (e.g., SRAM, DRAM, etc.) utilizing verticaltransport FinFET devices.

In various embodiments, the materials and layers can be deposited byphysical vapor deposition (PVD), chemical vapor deposition (CVD), atomiclayer deposition (ALD), molecular beam epitaxy (MBE), or any of thevarious modifications thereof, for example, plasma-enhanced chemicalvapor deposition (PECVD), metal-organic chemical vapor deposition(MOCVD), low pressure chemical vapor deposition (LPCVD), electron-beamphysical vapor deposition (EB-PVD), and plasma-enhanced atomic layerdeposition (PEALD). The depositions can be epitaxial or hetero-epitaxialprocesses, and the deposited material can be crystalline. In variousembodiments, formation of a layer can be by one or more depositionprocesses, where, for example, a conformal layer may be formed by afirst process (e.g., Thermal ALD, PEALD, etc.) and a fill may be formedby a second process (e.g., CVD, electrodeposition, PVD, etc.).

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps can be varied within the scope of the present invention.

It should be noted that certain features may not be shown in all figuresfor the sake of clarity. This is not intended to be interpreted as alimitation of any particular embodiment, or illustration, or scope ofthe claims.

Reference to source/drain projections, layers, regions, etc., isintended to indicate that the particular device feature can beimplemented as a source or a drain except as expressly indicatedotherwise, for example, by specific reference to a component as a sourceor a drain. In addition, the role of source and drain for an activedevice can in some instances be reversed, so a previously indicateddrain may instead be a source and vice versa. Reference to asource/drain is, therefore, intended to encompass the broadestreasonable scope of the term.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a cross-sectional side viewof a substrate is shown, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a substrate 110 can be a semiconductor or aninsulator with an active surface semiconductor layer. The substrate caninclude a carrier layer that provides structural support to otherlayers. The substrate can include crystalline, semi-crystalline,microcrystalline, or amorphous regions. The substrate can be essentially(i.e., except for contaminants) a single element (e.g., silicon),primarily (i.e., with doping) of a single element, for example, silicon(Si) or germanium (Ge), or the substrate can include a compound, forexample, Al₂O₃, SiO₂, GaAs, SiC, or SiGe. The substrate can also havemultiple material layers, for example, a semiconductor-on-insulatorsubstrate (SeOI), such as, a silicon-on-insulator substrate (SOI),germanium-on-insulator substrate (GeOI), orsilicon-germanium-on-insulator substrate (SGOI). The substrate can alsohave other layers forming the substrate, including high-k oxides and/ornitrides. The substrate may also include other previously fabricateddevices and features.

In one or more embodiments, the substrate 110 can be a silicon wafer. Invarious embodiments, the substrate can be a single crystal silicon (Si),silicon germanium (SiGe), or III-V semiconductor (e.g., GaAs) wafer, orhave a single crystal silicon (Si), silicon germanium (SiGe), or III-Vsemiconductor (e.g., GaAs) surface/active layer.

In various embodiments, the substrate 110 can provide the material forforming one or more vertical fin(s), where the vertical fin(s) can forma channel of a fin field effect transistor (FinFET), where the FinFEtcan be a vertical transport FinFET. A material layer different from thematerial of the substrate surface or carrier layer can be formed on thesurface, for example, a silicon-germanium layer on a single crystalsilicon surface to form a strained surface active layer to provide thematerial for forming one or more vertical fin(s) 111, where the surfaceactive layer can be part of the substrate 110.

FIG. 2 is a cross-sectional side view showing a fin template layerformed on the surface of the substrate, and a fin mask layer formed onthe fin template layer, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a fin template layer 120 can be formed on atleast a portion of a surface of a substrate 110. In various embodiments,the fin template layer 120 can be formed on the substrate surface byCVD, PECVD, PVD, thermal growth, or combinations thereof, where the fintemplate layer 120 can be blanket deposited on the substrate.

In one or more embodiments, the fin template layer 120 can have athickness in the range of about 20 nm to about 70 nm, or in the range ofabout 20 nm to about 50 nm, or in the range of about 50 nm to about 70nm, or in the range of about 30 nm to about 60 nm, where the thicknessof the fin template layer 120 can define the height of subsequentlyformed source/drain projections. Other thicknesses are alsocontemplated.

In various embodiments, a fin template layer 120 can be a hard masklayer for masking the substrate during transfer of a vertical finpattern to the substrate 110. The fin template layer 120 can be siliconoxide (SiO), silicon nitride (SiN), silicon oxynitride (SiON), siliconcarbonitride (SiCN), silicon boronitride (SiBN), silicon carbide (SiC),silicon borocarbide (SiBC), silicon boro carbonitride (SiBCN), boroncarbide (BC), boron nitride (BN), titanium nitride (TiN), orcombinations thereof, where the fin template layer 120 may include oneor more layers. The fin template layer 120 can also act as an etch-stoplayer, where the fin template layer 120 can be selectively etchedrelative to other layers.

In one or more embodiments, a fin mask layer 130 can be formed on thefin template layer 120, where the fin mask layer 130 can be a hard masklayer or soft mask layer for masking the fin template layer 120. In oneor more embodiments, the fin mask layer 130 can be a lithographic resistmaterial (e.g., a photo resist material, an e-beam resist material,etc.).

In one or more embodiments, the fin mask layer 130 can be a positive ornegative resist material, for example, Poly(methyl methacrylate) (PMMA)or SU-8, or an electron-beam (e-beam) cured material, for example,hydrogen silsesquioxane (HSQ).

In one or more embodiments, the fin mask layer 130 can be formed on thefin template layer 120 by a spin on process.

FIG. 3 is a cross-sectional side view showing a patterned fin mask layeron a patterned fin template layer, in accordance with an embodiment ofthe present invention.

In one or more embodiments, the fin mask layer 130 can be patterned anddeveloped to form a fin mask segment 131 on the fin template layer 120,where the fin mask segment 131 covers a portion of the fin templatelayer 120 and exposes other portions of the fin template layer. The finmask layer 130 can be patterned and developed using processes known inthe art. A plurality of fin mask segments 131 can form a fin pattern onthe fin template layer 120.

In one or more embodiments, the fin pattern formed by the fin masksegment(s) 131 can be transferred to the fin template layer 120 byremoving the exposed portion of the fin template layer 120. In variousembodiments, a portion of the fin template layer 120 can be removed toform a fin template 121 below each of the one or more fin masksegment(s) 131 by a directional reactive ion etch (RIE). Removal of theportions of the fin template layer 120 can expose portions of theunderlying substrate 110 or surface/active layer(s) between each of thefin mask segments 131 and fin templates 121. The lateral dimensions ofthe fin mask segments 131 and fin templates 121 can define the lateraldimensions of a top surface of a vertical fin.

FIG. 4 is a cross-sectional side view showing a vertical fin formed onthe substrate with a fin template and a fin mask segment on the verticalfin, in accordance with an embodiment of the present invention.

In one or more embodiments, one or more vertical fin(s) 111 can beformed on the substrate 110 or a surface active layer, where thevertical fin(s) 111 can be formed by removing a portion of the substrate110 between and/or around the fin mask segment(s) 131 and fintemplate(s) 121. One or more vertical fin(s) 111 can be formed by adirectional etch, for example, a reactive ion etch (RIE) that removesthe portion of the substrate 110 or surface active layer not covered bythe fin mask segment(s) 131 and fin template(s) 121. The removal of thesubstrate material can form vertical fin(s) 111 with a tapered profilehaving a greater length and width at the base 112 of the vertical fin(s)and a shorter length and narrower width at the top surface 113 of thevertical fin(s) 111, or with a straight profile (i.e., an essentiallyuniform width), where the tapered profile can be produced as an aspectof the etching process (e.g., control of reactants and/or processingparameters).

In one or more embodiments, the surface area of the top surface 113,A_(ts), of a vertical fin 111 in contact with a bottom surface of a fintemplate 121 can be less than the cross-sectional area of the base 112,A_(bcr), of the vertical fin at the plane of the substrate surface 99(Ats<A_(bcr)) adjacent to the vertical fin. The top surface 113 and base112 can be parallel. The vertical fin 111 includes two sidewallsseparated by a thickness, and two end walls separated by a length, andwherein the end walls can taper from the base of the fin to the top ofthe fin, such that the end walls 114 of the vertical fin 111 can form anobtuse angle, Θ₁, between the end wall 114 and substrate surface.

In various embodiments, the area at the top of the vertical fin may bemeasured as a cross-sectional area, A_(tcr), when the top surface is notuniform or not easily determined. The measurements of A_(ts) or A_(tcr),and A_(bcr) can be in a plane that is normal to the direction ofextension of the vertical fin from the substrate surface. In variousembodiments, the plane of the cross-sectional area, A_(bcr), of the base112 of the vertical fin and plane of the cross-sectional area, A_(tcr),are parallel, and separated by a distance less than or equal to theheight of the vertical fin 111. The height of the plane of thecross-sectional area, A_(tcr), from the base 112 can be at a distancewhere a further increase in height results in an accelerating decreasein the cross-sectional area compared to a previously steady decrease inthe cross-sectional area for a vertical fin that does not have a flat,uniform top surface (e.g., a negative second derivative (curved surface)compared to a zero negative derivative (constant slope)). In variousembodiments, the height of the plane of the cross-sectional area,A_(tcr), from the base 112 can be at least 95% of the perpendiculardistance from the base 112 to a highest point of the vertical fin 111.

The substrate 110 may have a doped region 119 below a vertical fin 111to form a bottom source/drain region. The doped region 119 may be formedin-situ or ex-situ below the vertical fin(s) 111. In variousembodiments, the doped region may be n-doped or p-doped. The dopedregion may be formed by ion implantation and annealed to form a bottomsource/drain. The vertical fin(s) 111 may be doped to have a doping type(e.g., n-doped or p-doped) opposite the doped region, or the verticalfin(s) 111 may be an intrinsic semiconductor to form a fully depletedchannel. The vertical fin(s) 111 may be doped in-situ or ex-situ.

FIG. 5 is a cross-sectional side view showing a spacer layer formed onthe vertical fin and fin template after removal of the fin mask segment,in accordance with an embodiment of the present invention.

In one or more embodiments, the fin mask segment(s) 131 can be removedusing processes known in the art, for example, ashing, stripping,chemical-mechanical polishing, etc. Removal of the fin mask segment(s)131 can expose the top surface of the fin template(s) 121.

In one or more embodiments, a bottom spacer layer 140 can be formed onthe fin template(s) 121, vertical fin(s) 111 and exposed surfaces of thesubstrate 110, where the bottom spacer layer 140 can be blanketdeposited by CVD, PECVD, PVD, high density plasma (HDP), gas cluster ionbeam (GCIB), enhanced High Aspect Ratio Process (eHARP), or combinationsthereof, or conformally deposited by ALD, PEALD, pulsed plasma CVD, orcombinations thereof.

In one or more embodiments, the bottom spacer layer 140 can be a siliconnitride (SiN), a carbon-doped silicon nitride (SiCN), a siliconoxynitride (SiON), silicon boro carbonitride (SiBCN), siliconoxycarbonitride (SiOCN), or combinations thereof. The silicon nitridecan include stoichiometric silicon nitride (Si₃N₄) and otherstoichiometric ratios of silicon and nitrogen.

In one or more embodiments, the bottom spacer layer 140 can have athickness in the range of about 1 nm to about 25 nm, or in the range ofabout 1 nm to about 10 nm, or about 1 nm to about 5 nm, although otherthicknesses are contemplated. The thickness of the spacer layer 140 onthe horizontal surfaces can be greater than the thickness on the slantedor vertical surfaces.

FIG. 6 is a cross-sectional side view showing a gate dielectric layerformed on a bottom spacer, vertical fin, and fin template after removalof the portion of the spacer layer on the vertical fin and fin template,in accordance with an embodiment of the present invention.

In one or more embodiments, a portion of the spacer layer 140 can beremoved from the vertical fin 111 and fin template 121, while a portionof the spacer layer 140 remains on the substrate surface 99 to form oneor more bottom spacers 141. In various embodiments, the portion of thespacer layer 140 can be removed can be removed using an isotropic etch(e.g., wet etch, dry plasma etch, etc.), where thinner portions of thespacer layer 140 can be removed to expose the end walls and sidewalls ofthe vertical fin(s) 111, while a portion of the spacer layer 140 remainson the substrate surface 99. The portion of the spacer layer 140 on thetop surface of the fin template 121 can be removed by using an organicplanarization layer (OPL) and a chemical-mechanical polishing (CMP)before performing an isotropic etch. The OPL can be removed after theCMP.

In one or more embodiments, a gate dielectric layer 150 can be formed onthe exposed surfaces of the fin template(s) 121, vertical fin(s) 111,and substrate 110, where the gate dielectric layer 150 can beconformally deposited by ALD, PEALD, CVD, PECVD, or combinationsthereof. The gate dielectric layer 150 can be formed on the end wallsand sidewalls of the vertical fin 111, such that the gate dielectriclayer forms a continuous layer around four sides of the vertical fin.

In one or more embodiments, the gate dielectric layer 150 can be aninsulating dielectric layer, for example, a silicon oxide (SiO), siliconnitride (SiN), silicon oxynitride (SiON), a high-K dielectric, or asuitable combination of these materials.

In various embodiments, the gate dielectric layer 150 can be a high-Kdielectric material that can include, but is not limited to, transitionmetal oxides such as hafnium oxide (e.g., HfO₂), hafnium silicon oxide(e.g., HfSiO₄), hafnium silicon oxynitride (Hf_(w)Si_(x)O_(y)N_(z)),lanthanum oxide (e.g., La₂O₃), lanthanum aluminum oxide (e.g., LaAlO₃),zirconium oxide (e.g., ZrO₂), zirconium silicon oxide (e.g., ZrSiO₄),zirconium silicon oxynitride (Zr_(w)Si_(x)O_(y)N_(z)), tantalum oxide(e.g., TaO₂, Ta₂O₅), titanium oxide (e.g., TiO₂), barium strontiumtitanium oxide (e.g., BaTiO₃—SrTiO₃), barium titanium oxide (e.g.,BaTiO₃), strontium titanium oxide (e.g., SrTiO₃), yttrium oxide (e.g.,Y₂O₃), aluminum oxide (e.g., Al₂O₃), lead scandium tantalum oxide(Pb(Sc_(x)Ta_(1-x))O₃), and lead zinc niobate (e.g., PbZn_(1/3)Nb_(2/3)O₃). The high-k material can further include dopants such aslanthanum and/or aluminum. The stoichiometry of the high-K compounds canvary.

In one or more embodiments, the gate dielectric layer 150 can have athickness in the range of about 1 nm to about 11 nm, or can have athickness in the range of about 2 nm to about 8 nm.

FIG. 7 is a cross-sectional side view showing a work function layer onthe gate dielectric layer, in accordance with an embodiment of thepresent invention.

In one or more embodiments, a work function layer 160 can be formed onthe exposed surfaces of the gate dielectric layer 150, where the workfunction layer 160 can be conformally deposited by ALD, PEALD, CVD,PECVD, or combinations thereof.

In one or more embodiments, a work function layer 160 can be formed onthe gate dielectric layer 150, where the work function layer 160 andgate dielectric layer 150 can surround at least a portion of each of oneor more vertical fin(s) 111 as a part of a gate structure. The workfunction layer 160 can be formed on the gate dielectric layer 150 toadjust the electrical properties of a gate electrode. In variousembodiments, the work function layer 160 can be optional.

In various embodiments, a work function layer 160 can be a conductivenitride, including but not limited to titanium nitride (TiN), titaniumaluminum nitride (TiAlN), hafnium nitride (HfN), hafnium silicon nitride(HfSiN), tantalum nitride (TaN), tantalum silicon nitride (TaSiN),tungsten nitride (WN), molybdenum nitride (MoN), niobium nitride (NbN);a conductive carbide, including but not limited to titanium carbide(TiC), titanium aluminum carbide (TiAlC), tantalum carbide (TaC),hafnium carbide (HfC); or combinations thereof. The work function layer160 can include multiple layers of work function materials, for example,a work function layer can be a TiN/TiC stack.

In various embodiments, the work function layer 160 can have a thicknessin the range of about 1 nm to about 11 nm, or can have a thickness inthe range of about 2 nm to about 8 nm.

FIG. 8 is a cross-sectional side view showing a gate fill layer on thework function layer, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a gate fill layer 170 can be formed on thegate dielectric layer 150 and/or work function layer 160 if present,where the gate fill layer 170 can fill in the space between verticalfins 111. The gate fill layer 170, gate dielectric layer 150, andoptionally the work function layer 160, can form a gate structure on oneor more vertical fin(s) 111, where the gate fill layer 170 and workfunction layer 160 can form a conductive gate electrode. The gatestructure formed on the fin can wrap around the two end walls and twosidewalls of each vertical fin 111 to cover at least a portion of thevertical fin forming a channel. The gate structure can be on the bottomspacer 141 and around a central portion of the vertical fin.

In various embodiments, the gate fill layer 170 can be a p-doped polysilicon (p-Si), an n-doped poly silicon (n-Si), a conductive metal,where the metal can be tungsten (W) or cobalt (Co), or a conductivecarbon material (e.g., carbon nanotube, graphene, etc.), or any suitablecombinations thereof. The gate fill layer 170 can be a heavily p-dopedpoly silicon to form a pFET, or a heavily n-doped poly silicon to forman nFET.

In one or more embodiments, the gate fill layer 170 can be blanketdeposited, and a chemical-mechanical polishing (CMP) used to remove gatefill layer material that extends above the top surfaces of the gatedielectric layer 150 and/or work function layer 160 if present, wherethe CMP can provide a smooth, flat surface.

FIG. 9 is a cross-sectional side view showing a gate structure with areduced height gate fill layer, in accordance with an embodiment of thepresent invention.

In one or more embodiments, the gate fill layer 170 and work functionlayer 160 if present, can be recessed to provide space for formation ofa subsequent top spacer layer. In various embodiments, each of the gatefill layer 170, gate dielectric layer 150 and/or work function layer 160can be partially removed using a selective etch (e.g., RIE). The gatefill layer 170, gate dielectric layer 150 and/or work function layer 160can be reduced to a depth equal to or below the fin template(s) 121 toprovide space for formation of top source/drains on the top surfaces ofthe vertical fin(s) 111. The height of the gate electrode can determinethe length of a channel in a vertical transport field effect transistor.In various embodiments, the gate structure can wrap around a middleportion of the vertical fin 111 to form a central gated region betweenthe base of the vertical fin and the top of the vertical fin. In variousembodiments, the gate structure 175 can cover a central ⅓ to ⅘ of thevertical fin height, or about a central ⅓ to about ⅔ of the vertical finheight, where the gate structure and fin height can determine theeffective gate length of a VTFET device.

FIG. 10 is a cross-sectional side view showing a gate structure formedon the vertical fin, and a top spacer formed on the exposed portions ofthe gate structure, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a top spacer layer 180 can be formed on thegate fill layer 170, gate dielectric layer 150 and/or work functionlayer 160 of the gate structure, where the top spacer layer 180 can beblanket deposited, for example, by CVD, PECVD, PVD, etc. In variousembodiments, the height of the top spacer layer 180 can be reduced, forexample, by CMP and/or an RIE, to equal to or below the bottom surfaceof the fin template 121.

In one or more embodiments, a top spacer layer 180 can be the samematerial used for the bottom spacer layer 140, or multiple layersthereof. In various embodiments, the top spacer layer 180 can be thickerthan the bottom spacer 141 to provide reduced channel-drain capacitance.

In one or more embodiments, an interlayer dielectric (ILD) layer 190 canbe formed on the top spacer layer 180, fin template 121, and gatedielectric layer 150. The ILD layer 190 can be silicon oxide (SiO), aflowable oxide, a polymeric material, a low-k dielectric, orcombinations thereof. A low-k dielelctric material can include, but notbe limited to, a fluoride-doped silicon oxide (e.g., fluoride dopedglass), a carbon doped silicon oxide, a porous silicon oxide, a spin-onsilicon based polymeric material (e.g., tetraethyl orthosilicate (TEOS),hydrogen silsesquioxane (HSQ) and methylsilsesquioxane (MSQ)), orcombinations thereof.

FIG. 11 is a cross-sectional side view showing a vertical fin with anexposed top surface after removal of the fin template, in accordancewith an embodiment of the present invention.

In one or more embodiments, a portion of the interlayer dielectric (ILD)layer 190 can be removed to expose the fin template 121, where the ILDlayer extending above the fin template 121 may be removed using CMP.

In one or more embodiments, the exposed fin template 121 can be removed,for example, by using a selective etch (e.g., RIE, wet etch, etc.) toexpose the top surface of the vertical fin 111. The vertical fin can bea single crystal material with a predetermined crystal face/orientationat the top surface.

FIG. 12 is a cross-sectional side view showing a top source/drain formedon the vertical fin, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a top source/drain 200 can be formed on thevertical fin 111, where the top source/drain 200 can be formed by anepitaxial growth process on a single crystal surface of the verticalfin. The top source/drain 20 may be suitably doped to form an n-type ora p-type FinFET device.

In various embodiments, a source is at the bottom of the vertical fin111 and a drain is at the top of the fin, such that the smaller surfaceor cross-sectional area at the top of the vertical fin 111 provides areduced drain-channel capacitance. The top source/drain 200 can be a topdrain, where the reduced contact area between the top drain and thesurface of the vertical fin can provide a reduced capacitance comparedto a vertical fin 111 with straight sidewalls and the samecross-sectional area at the top and bottom of the vertical fin. A fullydepleted channel can be between the bottom source and top drain, andsurrounded by central gated region.

FIG. 13 is an orthographic cut-away view of an exemplary vertical finhaving inclined end walls and sidewalls tapering inwardly in thedirection of the top surface, and a gate structure and top spacer on thevertical fin, in accordance with an embodiment of the present invention.

In one or more embodiments, the contact area between a vertical fin 111and a top drain 200 may be reduced by forming the vertical fin with oneor more tapered side or end walls ending at a smaller truncated topportion. The contact area between a vertical fin and a top drain mayalso be reduced by removing portions of the vertical fin at theinterface between a VTFET channel and the top drain. In variousembodiments, a portion of a vertical fin 111 including a section of thetop surface may be removed to a predetermined depth to reduce thecontact area between the top drain 200 and the top surface of the VTFETchannel to thereby reduce the capacitance at the channel-draininterface. The top spacer 180 can be formed on the gate fill layer 170of the gate structure 175 to electrically insulate the conductive gateelectrode from the top drain 200. The top spacer 180 can be on a portionof the vertical fin 111. A bottom spacer 141 can physically separate andelectrically isolate the gate structure 175 from the substrate 110including a doped region 119 below a vertical fin that can form a bottomsource. A gate dielectric layer 150 can be formed on the bottom spacerand a portion of the vertical fin 111. A work function layer 160 can beformed on the gate dielectric layer 150. The gate structure can be onthe tapered end walls and sidewalls of the vertical fin 111, where thethickness of the gate fill layer increases going from the base of thevertical fin to the top.

FIG. 14 is a cross-sectional side view showing a plurality of fin masksegments on each of a plurality of fin template segments patterned toform a series of masked regions, in accordance with an embodiment of thepresent invention.

In one or more embodiments, the fin mask layer 130 and fin templatelayer 120 can be patterned on the substrate 110 to form a series ofmasked regions on a portion of the substrate predetermined to form asingle vertical fin 111. The plurality of fin mask segments 131 and fintemplate segments 121 can be formed instead of one continuous fin masksegment 131 and fin template segment 121 on a surface of the substrateintended to form a vertical fin 111. The fin mask segments 131 and fintemplate segments 121 can have a predetermined width, W₁, and apredetermined spacing, S₁, that define portions of thesubstrate/vertical fin to be removed to form notches that reduce thearea of the top surface, A_(ts), or top cross-sectional area, A_(tcr).In various embodiments, W₁ and S₁ can be the same distance or differentdistances. In various embodiments, each fin mask segment 131 and fintemplate segment 121 can have a different width than other fin masksegments 131 and fin template segments 121 on the same portion of thesubstrate. The spacing between the fin template segments 121 can also bedifferent.

FIG. 15 is a cross-sectional side view showing a vertical fin formed onthe substrate with fin template segments and fin mask segments separatedby gaps, and notches formed in an upper portion of the vertical fin, inaccordance with an embodiment of the present invention.

In one or more embodiments, a vertical fin 111 can be formed by removinga portion of the substrate 110 between and/or around the plurality offin mask segments 131 and fin templates 121, where a directional etch,for example, a reactive ion etch (RIE) can remove exposed portions ofthe substrate 110 or surface active layer not covered by the fin masksegments 131 and fin templates 121. The removal of the substratematerial can form vertical fin(s) 111 with a tapered profile having agreater length and width at the base 112 and a shorter length andnarrower width at the top surface 113, and notches at the bottom of thegaps between the fin template segments and fin mask segments. Theangles, θ₁ and θ₂, can be controlled by the etching process.

The predetermined spacing, S₁, can influence the depth, D₁, of thenotch(es) 210 formed in the vertical fin 111, where the formation of anend wall or a notch 210 can depend on the predetermined spacing, S₁,between the fin templates 121. The depth, D₁, of the notches can alsodepend on the spacing, S₁, between the fin templates 121, where narrowerspacing can reduce the depth of the formed notch 210, and on theparameters of the etching process used to form the notch 210.

In one or more embodiments, notches 210 can be formed in the verticalfin 111 between fin templates 121 to a depth, D₁, of less than ½ theheight of the vertical fin, or to a depth of less than ⅓ the height ofthe vertical fin, or to a depth about equal to the thickness of a topspacer 180.

In one or more embodiments, the surface area of the top surface 113,A_(ts), or top cross-sectional area, A_(tcr), of the vertical fin 111 incontact with a bottom surface of a fin template 121 can be less than thecross-sectional area of the base 112, A_(bcr), of the vertical fin atthe plane of the substrate surface 99 (A_(ts) or A_(tcr)<A_(bcr))adjacent to the vertical fin. The presence of one or more notch(es) 210can further reduce the surface area of the top surface 113, A_(ts), ortop cross-sectional area, A_(tcr), measured near the top surface 113.The surface area, A_(ts), or cross-sectional area, A_(tcr), at the topof the fin can be in the range of about 10% to about 75% of thecross-sectional area at the base 112 of the fin, A_(bcr), or in therange of about 10% to about 60% of the cross-sectional area at the base112 of the fin, A_(bcr), or in the range of about 20% to about 45% ofthe cross-sectional area at the base 112 of the fin, A_(bcr). Theconfiguration and geometry of the vertical fin 111 can determine thereduction in the surface area of the top surface 113, A_(ts), or topcross-sectional area, A_(tcr), in relation to the cross-sectional areaat the base 112 of the fin, A_(bcr).

In one or more embodiments, the notches 210 can have an angled wall 215,where the angle, Θ₂, of the wall with a bottom surface 218 of the notchcan be determined by the parameters of the etching process used to formthe notch 210. In various embodiments, the notch 210 can have anessentially flat bottom surface 218 due to the etching process.

FIG. 16 is a cross-sectional side view showing a spacer layer formed onthe vertical fin, fin templates, and in the gaps and notches afterremoval of the fin mask segments, in accordance with an embodiment ofthe present invention.

In one or more embodiments, the fin mask segment(s) 131 can be removedusing processes known in the art, for example, ashing, stripping,chemical-mechanical polishing, etc. Removal of the fin mask segment(s)131 can expose the top surface of the fin template(s) 121.

In one or more embodiments, a spacer layer 140 can be formed on the fintemplate(s) 121, vertical fin(s) 111 and exposed surfaces of thesubstrate 110, where the spacer layer can also fill in the gap(s) 205between the fin templates 121 and fin mask segments 131, and thenotch(es) 210 in the top portion of the vertical fin(s) 111. The spacerlayer 140 can be formed by a directional, blanket deposition, where thethickness of the spacer layer is greater on surfaces parallel with thesubstrate surface 99, and thinner on surfaces angled or perpendicular tothe substrate surface 99. The spacer layer 140 can form dielectricplug(s) 220 in the one or more notch(es) 210 and gap(s) 205.

In various embodiments, a portion of the spacer layer 140 that extendsabove the top surfaces of the fin templates 121 can be removed, forexample, by CMP or etching. The spacer layer 140 can be an insulatingdielectric material, where the spacer layer 140 can be silicon oxide(SiO), a high-k dielectric, or a low-k dielectric material.

In various embodiments, the notch(es) 210 can be filled with adielectric material to form the dielectric plug(s) 220. In variousembodiments, the dielectric plug(s) 220 are filled with a low-k materialto reduce capacitance between the channel, gate structure, and topdrain.

FIG. 17 is a cross-sectional side view showing a gate dielectric layerformed on a bottom spacer, vertical fin, and fin template after removalof the portion of the spacer layer on the vertical fin and fin template,in accordance with an embodiment of the present invention.

In one or more embodiments, a portion of the spacer layer 140 can beremoved from the vertical fin 111, fin template 121, and an upperportion of gap(s) 205, while a portion of the spacer layer 140 remainson the substrate surface 99 to form one or more bottom spacers 141, andin the notch(es) 210 to form the dielectric plug(s) 220. In variousembodiments, the portion of the spacer layer 140 can be removed using anisotropic etch (e.g., wet etch, dry plasma etch, etc.), where thinnerportions of the spacer layer 140 can be removed to expose the end wallsand sidewalls of the vertical fin(s) 111, while a portion of the spacerlayer 140 remains on the substrate surface 99 and in the gap(s) andnotch(es) 210. The portion of the spacer layer 140 on the top surface ofthe fin template 121 can be removed by a chemical-mechanical polishingbefore performing an isotropic etch.

In one or more embodiments, a gate dielectric layer 150 can be formed onthe exposed surfaces of the fin template(s) 121, vertical fin(s) 111,and bottom spacers 141, where the gate dielectric layer 150 can beconformally deposited by ALD, PEALD, CVD, PECVD, or combinationsthereof. The gate dielectric layer 150 can be formed on the exposedsurfaces of the dielectric plug(s) 220.

In one or more embodiments, the gate dielectric layer 150 can be aninsulating dielectric layer, for example, a silicon oxide (SiO), siliconnitride (SiN), silicon oxynitride (SiON), a high-k dielectric, or asuitable combination of these materials.

FIG. 18 is a cross-sectional side view showing a work function layer onthe gate dielectric layer, in accordance with an embodiment of thepresent invention.

In one or more embodiments, a work function layer 160 can be formed onthe exposed surfaces of the gate dielectric layer 150, where the workfunction layer 160 can be conformally deposited by ALD, PEALD, CVD,PECVD, or combinations thereof.

In one or more embodiments, a work function layer 160 can be formed onthe gate dielectric layer 150, where the work function layer 160 andgate dielectric layer 150 can surround at least a portion of each of oneor more vertical fin(s) 111 as a part of a gate structure. The workfunction layer 160 and gate dielectric layer 150 also can be on oppositefaces of the dielectric plug(s) 220 in the upper portion of the verticalfin(s) 111.

FIG. 19 is a cross-sectional side view showing a gate fill layer on thework function layer, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a gate fill layer 170 can be formed on thegate dielectric layer 150 and/or work function layer 160 if present,where the gate fill layer 170 can fill in the space between verticalfins 111. The gate fill layer 170, gate dielectric layer 150, andoptionally the work function layer 160, can form a gate structure on oneor more vertical fin(s) 111, where the gate fill layer 170 and workfunction layer 160 can form a conductive gate electrode. The gatestructure formed on the vertical fin 111 can wrap around the two endwalls and two sidewalls of each vertical fin 111 to cover at least aportion of the vertical fin forming a channel.

FIG. 20 is a cross-sectional side view showing a gate structure with areduced height gate fill layer, in accordance with an embodiment of thepresent invention.

In one or more embodiments, the gate fill layer 170 and work functionlayer 160 if present, can be recessed to provide space for formation ofa subsequent top spacer layer. In various embodiments, each of the gatefill layer 170, gate dielectric layer 150 and/or work function layer 160can be partially removed using a selective etch (e.g., RIE). The gatefill layer 170, gate dielectric layer 150 and/or work function layer 160can be reduced to a depth equal to or below the fin template(s) 121 toprovide space for formation of a top spacer, and top source/drains onthe top surfaces of the vertical fin(s) 111. The height of the gateelectrode can determine the length of a channel in a vertical transportfield effect transistor (VTFET). In various embodiments, the gatestructure can wrap around a middle portion of the vertical fin 111. Thegate structure can cover at least a portion of the dielectric plug(s)220, where the notch(es) 210 have been formed to a depth, D₁, below thetop surface of the gate fill layer 170 and gate structure. The presenceof the dielectric plug(s) 220 within the VTFET channel surrounded by thegate structure can alter the electrical properties of the channel.

FIG. 21 is a cross-sectional side view showing a gate structure formedon the vertical fin, and a top spacer formed on the exposed portions ofthe gate structure, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a top spacer layer 180 can be formed on thegate fill layer 170, gate dielectric layer 150 and/or work functionlayer 160 of the gate structure, where the top spacer layer 180 can beblanket deposited, for example, by CVD, PECVD, PVD, etc. In variousembodiments, the height of the top spacer layer 180 can be reduced, forexample, by CMP and/or an RIE, to equal to or below the bottom surfaceof the fin template 121. The top surface of the top spacer layer 180 canbe level with the top surface of the vertical fin 111.

In one or more embodiments, the top spacer layer 180 can be a siliconnitride (SiN), a carbon-doped silicon nitride (SiCN), a siliconoxynitride (SiON), silicon boro carbonitride (SiBCN), siliconoxycarbonitride (SiOCN), or combinations thereof. The silicon nitridecan include stoichiometric silicon nitride (Si₃N₄) and otherstoichiometric ratios of silicon and nitrogen.

In one or more embodiments, a top spacer layer 180 can be the samematerial or used for the bottom spacer layer 140, a different material,or multiple layers thereof.

In one or more embodiments, an interlayer dielectric (ILD) layer 190 canbe formed on the top spacer layer 180, fin template 121, and gatedielectric layer 150. The ILD layer 190 can be silicon oxide (SiO), aflowable oxide, a polymeric material, a low-k dielectric, orcombinations thereof. A low-k dielelctric material can include, but notbe limited to, a fluoride-doped silicon oxide (e.g., fluoride dopedglass), a carbon doped silicon oxide, a porous silicon oxide, a spin-onsilicon based polymeric material (e.g., tetraethyl orthosilicate (TEOS),hydrogen silsesquioxane (HSQ) and methylsilsesquioxane (MSQ)), orcombinations thereof.

FIG. 22 is a cross-sectional side view showing a vertical fin with anexposed top surface and dielectric plugs after removal of the fintemplates, in accordance with an embodiment of the present invention.

In one or more embodiments, a portion of the interlayer dielectric (ILD)layer 190 can be removed to expose the fin template 121, where the ILDlayer extending above the fin template 121 may be removed using CMP.

In one or more embodiments, the exposed fin templates 121 can beremoved, for example, by using a selective etch (e.g., RIE, wet etch,etc.) to expose the top surface of the vertical fin 111 on oppositesides of a dielectric plug 220. The vertical fin 111 can be a singlecrystal material with a predetermined crystal orientation at the topsurface.

In one or more embodiments, the upper portion of the dielectric plug 220previously in the gap(s) 205 can be removed by a selective, directionaletch (e.g., RIE) to reduce the height of the dielectric plug 220 to thelevel of the top surface of the vertical fin 111.

FIG. 23 is a cross-sectional side view showing a top source/drain formedon the vertical fin, in accordance with an embodiment of the presentinvention.

In one or more embodiments, a top source/drain 200 can be formed on theexposed portions of the top surface 113 of the vertical fin 111, wherethe top source/drain 200 can be formed by an epitaxial growth process ona single crystal surface of the vertical fin. The top source/drain 200may be suitably doped to form an n-type or a p-type FinFET device.

In various embodiments, the top source/drain 200 can be formed on thedielectric plug(s) 220, where the top source/drain 200 spans thedistance between exposed surface portions of the vertical fin 111.

FIG. 24 s a cross-sectional side view showing void spaces formed byremoval of the dielectric plugs, and a top source/drain formed on thevertical fin across the void spaces, in accordance with an embodiment ofthe present invention.

In one or more embodiments, the dielectric plug 220 may be selectivelyremoved using an isotropic etch (e.g., a wet etch) to form void spaces222 within the vertical fin 111 between a channel and the top drain 200,where the void spaces 222 reduce the channel-drain capacitance, sinceair has a lower dielectric constant (i.e., k=1) compared to thedielectric constant of the material forming the dielectric plug(s) 220.

FIG. 25 is an orthographic cut-away view of an exemplary vertical finhaving inclined end walls and sidewalls, and notches formed in the upperportion and top surface of the vertical fin, in accordance with anembodiment of the present invention.

In one or more embodiments, a vertical fin 111 on a substrate 110, mayhave a base 112 with a length, L₁ (forming a long axis), and a topsurface 124 with a length, L₂, where L₂<L₁, a width (forming a shortaxis), and a height from the top surface 113 of the vertical fin 111 tothe base 112 of the fin at the surface 99 of the substrate 110. An edgeof a sidewall may taper inwards from the base 112 of the vertical fin111 to the top surface 113, forming a trapezoidal sidewall joining withinclined end walls. The end wall(s) can form the channel angle, θ₁, tothe substrate surface 99, where θ₁ may be an angle describing the degreeof inclination from a source to a drain. The channel angle, θ₁, may bean obtuse angle (i.e., >90°). The angle of inclination, θ₁, may be thesame or different for each of the end walls. The notches 210 can haveflat or pointed bottoms.

In various embodiments, a vertical fin 111 may have two sidewalls 114separated by a width (i.e., thickness) and two end walls 116 separatedby a length, where an edge of the end wall(s) may taper inwards from thebase 112 of the vertical fin 111 to the top surface 113, forming atrapezoidal end wall joining with inclined sidewalls 114.

In various embodiments, the end walls 116 and sidewalls 114 may bothtaper inwards to form a pyramidal vertical fin 111, where thecross-sectional area at the interface of the base 112 of the verticalfin 111 with the substrate 110 is greater than the cross-sectional areaat the interface of the top of the vertical fin and a top drain. The endwalls 116 and/or sidewalls 114 may not be perpendicular to the substratesurface 99.

In one or more embodiments, a portion of the vertical fin 111 can beremoved from a section along the top surface 113 to form a notch 210.The notch 210 may extend from the top surface 113 downward towards thebase 112 of the vertical fin 111, where the notch 210 may have a widthand a depth from the top surface 113. In various embodiments, the notch210 spans the width of the vertical fin 111, but does not extend to thesurface 99 of the substrate 110, instead the notch 210 ends above thebase 112 of the vertical fin 111. The lowest point of the notch 210 maybe above the midpoint of the height of the vertical fin 111. In variousembodiments, the notch 210 may have a V-shape or truncated V-shapeetched into the top surface 113 of the vertical fin 111.

The notch 210 may be rectangular, wedge-shaped, truncated wedge-shaped,semi-cylindrical, D-shaped, or any other shape suitable for reducing thecontact area between a top drain and the top surface of the VTFETchannel without penetrating to the level of the substrate. If the notch210 has planar sidewalls, the sidewalls may form an angle of θ₂ witheach other or with a flat bottom surface 218 of the notch 210.

In one or more embodiments, a plurality of notches 210 may be formed inthe vertical fin(s) 111, where the notches 210 may be placedsymmetrically along the top surface 113, such that the distance betweenneighboring notches 210 are equidistant from each other and the edge ofthe top surface 113 that meets with an end wall 116, or asymmetricallyalong the top surface 113, such that the distances between neighboringnotches 210 are not equidistant from each other and/or the edge of thetop surface 113 that meets with an end wall 116. The notches 210 may bealigned approximately parallel (e.g., ±2°, ±1°, or ±0.5°) with the shortaxis (i.e., width) of the vertical fin 111.

In various embodiments, the cross-sectional area at the top of the finis in the range of about 10% to about 75% of the cross-sectional area,or about 10% to about 60% of the cross-sectional area at the base of thefin, or about 15% to about 50% of the cross-sectional area at the baseof the fin, or about 20% to about 45% of the cross-sectional area at thebase of the fin, where the total cross-sectional or surface area can bethe sum of two or more areas (e.g., A₁, A₂, A₃, etc.) separated bynotches 210.

In one or more embodiments, a vertical fin 111 can have across-sectional area, A_(bcr), at the base of the vertical fin, and across-sectional area, A_(ts), at the top surface 113 of the verticalfin, where the cross-sectional area, A_(ts), may be the sum ofcross-sectional areas, A₁+A₂+A₃+A_(n), etc., for each individual area atthe top of the vertical fin separated by an intervening notch 210. Thecross-sectional area, A_(bcr), at the base 112 of the vertical fin thatmay be larger than a cross-sectional area, A_(ts), at the top surface ofthe fin (A_(bcr)>A_(ts)). The sum of A₁, A₂, A₃, etc. can, therefore, beabout 10% to about 75% or about 10% to about 60% of the cross-sectionalarea at the base, A_(bcr), of the vertical fin 111. One or more notchesin the vertical fin can reduce the surface area at the top of thevertical fin by about 40% to about 70% compared to the cross-sectionalarea at the top of the vertical fin without one or more notches.

In a non-limiting example of a vertical transport finFET structure, avertical fin can form a channel with inclined endwalls and a pluralityof wedge-shaped portions removed from an upper section of the verticalfin to form notches.

FIG. 26 is a block/flow diagram illustrating a method of forming a VTFETwith reduced drain capacitance and reduced source resistance, inaccordance with an embodiment of the present principles.

A VTFET may be fabricated by a method 500 that provides a smallercross-sectional area at the top of the vertical fin than at the base ofthe vertical fin.

In block 510, a dopant may be introduced into at least a region of asubstrate on which a VTFET device may be fabricated. The dopant may beintroduced into the substrate to form a bottom source for a vertical findevice, where a doped region may be formed and annealed to activate thedopants to form the bottom source. In various embodiments, a drain isnot formed in the substrate for the VTFET device.

In various embodiments, the bottom source may be doped in-situ orex-situ, for example, through ion implantation or thermal diffusion ofdopants into the substrate. The dopant of the source may be activated byannealing. Other suitable doping techniques may also be used, includingbut not limited to, gas phase doping, plasma doping, plasma immersionion implantation, cluster doping, infusion doping, liquid phase doping,solid phase doping, or combinations thereof.

In block 520, one or more vertical fins may be formed on the substrate,where the vertical fins may be formed by a sidewall image transfer (SIT)process, for example, self-aligned double patterning (SADP), orself-aligned quadruple patterning (SAQP). An active semiconductor layermay be epitaxially grown on the substrate to a predetermined thickness,where the source may be buried beneath the active layer. A fin templatelayer, which may be a hardmask layer, may be formed on the active layer.A mandrel layer may be formed on the fin template layer, where themandrel layer can be, for example, amorphous silicon orsilicon-germanium, for forming dummy mandrels. A mandrel template layercan be formed on the mandrel layer, where the mandrel template layer canbe a hardmask layer. A softmask layer can be formed on the mandreltemplate layer, where the softmask layer can be patterned and developedto form a mandrel pattern exposing portions of the mandrel templatelayer. The mandrel pattern can be transferred from the softmask layer tothe mandrel template layer and mandrel layer by anisotropic directionaletching, for example, a dry plasma etch or reactive ion etch (RIE), toform one or more dummy mandrels. Spacers can be formed on the sidewallsof the mandrels, for example, by a blanket or conformal deposition andetch back. The spacers can form a fin pattern that may be transferred tothe fin template layer to form fin templates and the active layer toform a plurality of vertical fins by RIE.

In one or more embodiments, formation of the vertical fins by RIE usingthe spacers and/or fin templates can provide a tapered profile or avertical profile by adjusting and/or controlling the etching process aswould be known in the art.

In block 530, vertical fins provided with a vertical profile in block520 may be further etched to provide a tapered profile, where theetching process may be selected or adjusted to achieve a predeterminedtaper angle, as would be known in the art.

In block 540, the vertical fins may be suitably masked and notchesformed in the top portion of the vertical fins. The notch(es) may beformed by etching away an exposed portion of the vertical fin to apredetermined depth, dimension, and profile.

In block 550, a dielectric material may be formed on the substrate andthe vertical fin to form a bottom spacer for the VTFET device. Thedielectric material may be blanket deposited over the substrate and mayfill in at least a portion of the notches to form a dielectric plug.

In block 560, a gate structure can be formed on the vertical fin bydepositing a gate dielectric layer on the bottom spacer and thesidewalls and end walls of the vertical fin. A conductive gate electrodemay be formed on the gate dielectric, where the gate electrode mayinclude a work function layer and/or a gate fill. The gate fill layercan be a metal, and the work function layer can be a conductive metalnitride, metal carbide, or combination thereof.

The gate dielectric layer and gate electrode may fill in at least aportion of one or more notches in the vertical fin.

In block 570, a dielectric fill may be formed on the gate structure andthe vertical fin to form a top spacer.

In one or more embodiments, a vertical transport FET may be fabricatedhaving a bottom source formed in the substrate 110, a vertical fin 111formed on the substrate above the bottom source, a gate contact can beelectrically coupled to a gate structure 175 on the vertical fin 111,and a top drain 200 can be on at least a portion of the top surface 113of the vertical fin 111.

In one or more embodiments, a vertical fin 111 may form a channel for avertical transport fin field effect transistor (VTFET), where currentflows vertically from a doped region forming a bottom source 119 in thesubstrate 110 through the vertical fin 111 forming the channel to a topdrain 200. A gate structure 175 can be formed on one or more of thesidewalls 114 and/or end walls 116 of the vertical fin, where the gatestructure 175 can form a central gated region between the base of thevertical fin and the top of the vertical fin configured to controlcurrent flow through the channel of the VTFET.

In one or more embodiments, the gate structure 175 can include a gatedielectric layer 150 on at least a portion of the vertical fin 111, anda conductive gate electrode on at least a portion of the gate dielectriclayer, where the gate dielectric layer electrically insulates the gateelectrode from the VTFET channel. The conductive gate electrode mayinclude a work function layer 160 and a gate fill layer 170, where thework function layer can be on at least a portion of the gate dielectriclayer, and the gate fill layer can be on at least a portion of the workfunction layer, such that the work function layer 160 may be between thegate dielectric layer and the gate fill layer.

Reference in the specification to “one embodiment” or “an embodiment”,as well as other variations thereof, means that a particular feature,structure, characteristic, and so forth described in connection with theembodiment is included in at least one embodiment. Thus, the appearancesof the phrase “in one embodiment” or “in an embodiment”, as well anyother variations, appearing in various places throughout thespecification are not necessarily all referring to the same embodiment.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements can also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements can be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

The present embodiments can include a design for an integrated circuitchip, which can be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer can transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein can be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements can be included in the compound and stillfunction in accordance with the present principles. The compounds withadditional elements will be referred to herein as alloys.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This can be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or including, when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or ore other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above”“upper,” and the like, can be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein can be interpreted accordingly. In addition, itwill also be understood that when a layer is referred to as being“between” two layers, it can be the only layer between the two layers,or one or more intervening layers can also be present.

It will be understood that, although the terms first, second, etc. canbe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

Having described preferred embodiments of a device and method (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope of the invention as outlined by the appended claims.Having thus described aspects of the invention, with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

What is claimed is:
 1. A vertical transport fin field effect transistor(VTFET) with a smaller cross-sectional area at the top of the fin thanat the bottom, comprising: a substrate; a vertical fin on the substrate,wherein the vertical fin has a cross-sectional area at the base of thevertical fin that is larger than a cross-sectional area at the top ofthe vertical fin, wherein the cross-sectional area at the top of thevertical fin is in the range of about 10% to about 75% of thecross-sectional area at the base of the vertical fin; and a centralgated region between the base and the top of the vertical fin.
 2. TheVTFET of claim 1, wherein the vertical fin includes two sidewallsseparated by a thickness, and two end walls separated by a length, andwherein the end walls taper from the base of the vertical fin to the topof the vertical fin forming an angle, with the surface of the substrate.3. The VTFET of claim 2, wherein the central gated region comprises agate structure formed on the vertical fin, wherein the gate structurewraps around the two end walls and two sidewalls of the vertical fin. 4.The VTFET of claim 1, wherein the vertical fin includes at least onenotch in the top of the vertical fin that reduces the cross-sectionalarea at the top surface of the vertical fin.
 5. The VTFET of claim 4,further comprising a dielectric plug in the at least one notch.
 6. TheVTFET of claim 1, wherein the cross-sectional area at the top of thevertical fin is in the range of about 20% to about 45% of thecross-sectional area at the base of the fin.
 7. The VTFET of claim 6,wherein one or more notches in the vertical fin reduces thecross-sectional area at the top of the vertical fin by about 40% toabout 70% compared to the cross-sectional area at the top of thevertical fin without one or more notches.
 8. The VTFET of claim 7,further comprising a fully depleted channel surrounded by central gatedregion.
 9. The VTFET of claim 8, further comprising a doped region inthe substrate forming a bottom source/drain at the bottom of thevertical fin, and a top source/drain on at least a portion of the top ofthe fin.
 10. The VTFET of claim 9, wherein a source is at the bottom ofthe vertical fin and the drain is at the top of the vertical fin, suchthat the smaller cross-sectional area at the top of the fin provides areduced drain-channel capacitance.
 11. A vertical transport fin fieldeffect transistor (VTFET) with a smaller cross-sectional area at the topof the vertical fin than at the base of the vertical fin, comprising: asubstrate; a doped region in the substrate forming a bottom source; anda vertical fin having two sidewalls separated by a thickness, and twoend walls separated by a length on the bottom source, wherein the endwalls taper from the base of the vertical fin adjacent to the bottomsource to the top of the vertical fin opposite the base and separated bya height of the vertical fin.
 12. The VTFET of claim 11, furthercomprising at least one notch in the top of the fin that reduces thecross-sectional area at the top of the fin.
 13. The VTFET of claim 12,wherein the at least one notch has angled sidewalls and a flat bottom.14. The VTFET of claim 13, further comprising a gate structure formed onthe vertical fin, wherein the gate structure wraps around the two endwalls and two sidewalls of the fin, and a dielectric material fills inat least a portion of the at least one notch.